Automobiles are so constructed that they form a floating assembly on rolling elements, i.e. the chassis is isolated from the wheels by flexible elements, such as leaf springs, torque arms, helical springs, rubber blocks, etc., which make the chassis, wherein the cab of the vehicle is erected, independent of the wheels and their axles, thereby contributing decidedly to the comfort of the passengers and/or to the security of the transported load.
In order to accomodate the diverse and brusque reactions of the flexible elements, it is necessary to arrange a control element between the chassis and the supports of the axles of the wheels, which control element is a shock absorber.
The shock absorber is incorporated to the vehicle by means of two anchors, one of which fixes the shock absorber to the axle of the wheels, and the other of which fixes the shock absorber to resistant points of the chassis of the vehicle.
The working cycle of the shock absorber is two stage, thus the use of the denomination of a "double effect" shock absorber. This working cycle differs, depending on the needs of the vehicle, which needs are imposed by the load and the features of the terrain over which the vehicle travels. One of the effects of the shock absorber is that of resistance to descent, while the other effect is that of retention from ascent.
The resistance effect is produced when the vehicle encounters in its travel a pothole and, consequently, the vehicle, the low wheel and the weight of the vehicle fall therein, which fall is controlled by the shock absorber so that movement can be produced smoothly.
The retention effect is produced as a result of the resistance effect, and is provoked by the suspension system which, after being compressed, distends, or attempts to return, violently in the opposite direction.
This violent return must be controlled by the shock absorber by damping the return movement so that it is produced very slowly.
From the above it can be seen that the function of the shock absorber is at all times to control the flexible effect of the suspension system, while joining the chassis of the vehicle to the axle of the wheels, thus forming a safe and stable assembly.
Conventionally, the double effect telescopic hydraulic shock absorber is constituted from two tubular, concentric bodies which form two chambers, i.e. inner and outer chambers. The inner chamber is cylindrical and is filled with oil, while the outer chamber is annular and constitutes an oil reservoir.
Both tubular bodies have a common base which closes them at one side, while at the other side they are provided with independent bases.
A piston moves along the interior of the central tubular body, which piston divides the inner chamber into two volume-defined inner chambers and which piston includes a double set of one-way, oppositely-acting valves.
The piston is attached to a rod which, in perfect adjustment, slides along a housing provided in the common base of the two tubular bodies, the rod having at the end thereof opposite to the piston, an anchor by which it is fixed to the chassis of the vehicle.
The outer tubular body has an anchor situated at the end thereof opposite to that along which the rod slides, by which the tubular body is fixed to the axle of the wheel.
The movements of the suspension system are transferred to the rod which makes the piston slide along the inner chamber.
The movement of the piston is impeded by the oil contained in the inner chamber, which oil is forced to pass from one to the other of the two chambers separated by the piston and forming the inner chamber.
This transfer from one chamber to the other occurs through the one-way, oppositely-acting valves provided in the piston.
When the piston advances, a portion of the oil is transferred from one inner chamber to the other, with the exception of an amount of oil which corresponds to the volume of the rod introduced in the other inner chamber. This amount of oil is expelled by a valve device towards the outer annular chamber and is subsequently recovered therefrom by suction when the piston is displaced in the opposite direction.
The valve device which connects the inner chamber and the annular chamber is arranged in the inner tubular body, and is precisely situated at the end thereof opposite the piston rod.
Evidently, the one-way valve device which opens when the piston advances towards the end opposite to the rod has a higher sensitivity than the one-way valve device which acts in the opposite direction. This is due to the fact that the advancement of the piston towards the end opposite the rod is effected when the frame and chassis are displaced towards the ground, that is when they are lowered. This movement is smoothly controlled by the suspension system of the vehicle in cooperation with the shock absorber. However, the displacement of the piston in the direction toward the rod end is effected when the vehicle tends to bounce, this bouncing being controlled by a higher resistance to oil passage.
As the rate of displacement of the vehicle increases, the function to be performed by the shock absorber also increases, thus adjusting the flexible effects of the suspension system, therefore requiring the shock absorber to effect a greater control of the suspension system, so that the effects of resistance to descent and retention from ascent are maintained.
When the effect of resistance to descent increases, damping becomes harder, and therefore travelling at a slow speed becomes uncomfortable. However, when the resistance effect diminishes, the suspension system becomes more comfortable when travelling at slow speeds. This gives rise to the fact that two types of telescopic shock absorbers are preferably used, one for use in sports cars and high speed vehicles and the other for conventional, slower use.